A work machine such as a hydraulic excavator is provided with a boom that is liftably mounted to a base machine, and an arm that is mounted at the tip end of the boom to be able to rotate about a horizontal axis. A plurality of pipes are mounted onto an upper plate of the boom or the like so as to extend along the boom or the arm. The respective pipes are used to guide a hydraulic oil for driving the arm and a work device at the tip end of the arm by hydraulic pressure.
In general, each of the boom and the arm has a tubular shape. The boom or the arm is manufactured by welding a pair of side plates to both sides of the long upper plate and lower plate. A block for fixing the pipes is welded and fixed to the surface of the upper plate. The pipes are fastened by bolts between the block that is fixed to the surface of the upper plate and a mounting bracket. Thereby, the pipes are fixed to the block.
According to the mounting structure of the pipes like this, strength is required in the upper plate of the boom, the arm or the like. However, the block for fixing the pipes is mounted onto the upper plate by the welding. For this reason, when bending stress or other stress is applied to the boom or the arm at the time of using the work machine, stress concentration may be caused at a welded end portion of the block. This may cause the possibility that fatigue strength is reduced at the periphery of the welded end portion of the upper plate of the boom or the arm.
Particularly, an attachment formed by a long boom and arm may be used in the work machine such as a demolition machine, a handling machine or the like. From the viewpoint of stability and the like at the time of using the work machine, it is necessary to reduce the weight by reducing the plate thickness of the upper plate and the like of the boom and the arm, or by reducing the cross section of the boom and the arm. Meanwhile, the long attachment is longer than a backhoe and the like, and it is likely that larger bending load or the like is applied to the long attachment. This may cause the stress concentration at the welded end portion of the block in the upper plate. Thereby, cracks may be caused in the upper plate of the boom or the arm in the periphery of the welded end portion. This causes such a problem that the reduction in weight is difficult to achieve.
The following measures have been proposed conventionally against the problem in fixing the pipes.
First, according to a pipe fixing structure of Patent Document 1, a long plate-shaped bridging member is provided to fix the pipes. Bending portions are provided at both ends of the bridging member. The bridging member is arranged along the upper plate of the boom in the width direction of the boom. The tip end of the bending portion at one end of the bridging member abuts against one of boom side plates. The tip end portion of a bolt screwed to a screw hole in the bending portion at the other end of the bridging member is pressed against the other boom side plate. Thus, the bridging member is fixed onto the upper side of the boom. With the configuration like this, the tip end of the bending portion at one end of the bridging member and the tip end of the bolt fixed to the bending portion at the other end clamp the boom from the both side surfaces, while a plurality of pipes are fixed to the bridging member in advance, so that the plurality of pipes can be fixed to the boom.
Further, according to a pipe fixing structure of Patent Document 2, a projection is formed by upwardly extending a part of a boom side plate. A plurality of through holes are formed in the projection. The tip end portions of fixtures, such as U-bolts, for fixing the pipes penetrate through the through holes. The tip end portions of the U-bolts are fastened by nuts.
According to the pipe fixing structure described in Patent Document 1, however, the boom is clamped from the both side surfaces by the bending portion of the bridging member and the bolt, and the pipes and the bridging member are fixed to the boom by the clamping force. However, the fixing method like this is less stable as compared with the fixing method such as the welding and the like. As a result of this, the bridging member may be displaced or fallen off from the boom, when the large bending load is applied to the boom at the time of operating the work machine. In addition, when the work device that produces strong vibration, such as a nibbler, a breaker or the like, is used as the work device to be mounted at the tip end of the arm, the bridging member may be displaced from the predetermined position due to pulsation of the hydraulic oil inside the pipes and the vibration transmitted through the pipes.
Further, in order to increase the clamping force of the bridging member, it is necessary to increase the cross section of the bridging member and to improve its rigidity. Therefore, the weight of the bridging member itself may be increased.
Meanwhile, according to the pipe fixing structure described in Patent Document 2, the projection is formed by upwardly extending a part of the boom side plate. The pipes are fastened to the projection by the fixtures such as the U-bolts. Even though the projection is formed on the both side plates of the boom in the structure like this, the number of the pipes that can be fixed to the projections is no more than two. Therefore, it is only a pair of pipes, forming a circuit of one reciprocation, or the like, that is fixed to the projections. Thus, it is difficult to fix the many pipes. In general, when the work device such as the nibbler, a grapple or the like that is driven by the hydraulic pressure is attached at the tip end of the long attachment, the many pipes are necessary to supply the hydraulic oil for operating such a work device (for example, four or five pairs of pipes are required to form a circuit of four or five reciprocations). However, according to the pipe fixing structure described in Patent Document 2, it is difficult to fix all the pipes to the projections.    Patent Document 1: Japanese Utility Model Application Laid-open No. S59-168086    Patent Document 2: Japanese Utility Model Application Laid-open No. S61-198352